Axial flow impellers are known, e.g. from the following documents WO 2010/103172 A1, WO 2010/059572 A1 and EP 0465636 B1. A blade of an axial flow impeller is connectable to a central hub of the impeller. The impeller comprises two or more such blades. The blade is formed from substantially plate-type material. The blade includes a leading edge, a trailing edge, a tip, and a root attachable to the central hub of the impeller. A straight first bend extends along the blade in a first direction and divides the blade into a first profile portion located adjacent to the leading edge and a second profile portion. The first and the second profile portions meet at the first bend such that the first profile portion is angled at a first angle downwardly from the second profile portion. A straight second bend extends along the blade in a second direction which is different from said first direction and located apart from the first bend. The second bend divides the blade further into a third profile portion located adjacent to the trailing edge. The second and third profile portions meet at said second bend such that the third profile portion is angled at a second angle downwardly from the second profile portion. The second profile portion is angled at a third angle in relation to horizontal plane.
In the market there are some known types of axial flow impellers commercially available that perform with reasonably good performance.
However, there is still a need for an even better axial flow impeller with low energy consumption and which still provides high pumping capacity and pumping efficiency. In many metallurgical applications (e.g. gold processes and storage tanks), there is a need for an axial flow impeller with as high pumping capacity as possible per shaft power. For gold processes it is also crucial that the impeller region is as free of high energy dissipation zones as possible as these would act to destroy the carbon which is used to collect the gold.
Therefore, it is desirable to provide an efficient axial flow impeller which performs well to satisfy process requirements with less power consumption, less residence time, higher pumping efficiency and less weight.
An object of the present invention is to provide a blade for an axial flow impeller which provides the axial flow impeller with better performance characteristics than the existing axial flow impellers. The object on the invention is also to provide a blade and axial flow impeller having a low power consumption and low operational cost, high pumping capacity and pumping efficiency and great pumping mass flow rate per unit of energy consumption. Further, the object is also to provide blade shape and scaling rules for the blade of the axial flow impeller that enable scaling up and down.